1. Field of the Invention
The invention concerns a method for providing the planar surface of an active face for magnetic recording/reading heads, the planar surface of the active face being obtained by grinding.
2. Description of the Prior Art
A magnetic reading and/or recording head is formed by a ring-shaped magnetic circuit cut by a narrow gap consisting of a non-magnetic material.
Magnetic heads can be classified under three major groups:
massive heads are made by machining and joining two semi-heads, made of magnetic material, such as video heads (VHS heads) or analog audio heads. These heads are coiled at the end of the fabrication method;
thin layer heads are made by successive deposition of magnetic, dielectrical and conductive materials. These layers undergo masking and etching operations which enable the magnetic circuit, the gap and the conductive turns to be obtained;
heads having, on either side of the gap, a magnetic metallic alloy with a thickness that varies between 0.1 and 40 micrometers, the rest of the magnetic circuit and the conductive turns being made in the same way as for the massive heads. These are so-called MIG (metal in gap) heads which are used today in 8 mm. or RDAT (rotary digital audio tape) systems.
In the method of fabrication of a magnetic recording/reading head, it is often necessary to machine a heterogeneous part, formed by the association of a magnetic material (ferrite for example) and a non-magnetic material (glass for example). This is the case, notably, for the fabrication of the magnetic head described in the French patent application by the present applicant, filed under No. 87 14824. If a magnetic thin layer has to be deposited on this machined head, as for the magnetic head described in the French patent application by the present applicant, filed under No. 87 14820, it is necessary to have an excellent surface quality.
However, during grinding of a heterogeneous part, the two materials forming this heterogeneous part wear out. This differential wear is all the greater when the materials have different hardness. This is particularly so in the case of ferrite which is usually ground with a mixture of diamond powder, and of glass which is usually ground with cerium oxide. The plane thus machined therefore has a defect due to the irregular surface which may be incompatible with the requirements of the following steps for making the magnetic head.
To overcome this problem, the invention proposes a new method of achieving the planar surface of an active face of magnetic recording/reading heads, which permits the deposition of a non-magnetic material on the active face, before the grinding operation.